Carbon black pigments have conventionally been employed for forming a black film. Carbon black pigments have a primary particle size as fine as 10 to 30 nm. As its particle size becomes smaller, the jet blackness level increases and the jet black color acquires more preferred aesthetic quality.
The black film obtained using carbon black however absorbs a solar light and changes it into heat energy so that a marked temperature increase occurs. When an automobile in a black color is left under the blazing sun in summer, the surface temperature of the film approaches even to 80° C. Infrared radiation of a sunlight having a wavelength as long as 700 nm or greater is known to be absorbed by carbon black in a film and converted into heat so that it is highly effective for raising the temperature of the film.
Thus, a film coated in black causes a drastic temperature increase out of doors compared with a film in another color. An automobile coated in black involves the problem of energy saving, because in summer, an air conditioner of such an automobile does not work well and much energy is used for cooling its inside. A member such as a fuel tank of a motorbike, which is brought into direct contact with the human skin, becomes too hot and there is a danger of a rider suffering a burn.
A black pigment which does not absorb infrared radiation and therefore hardly generates heat has been developed. For example, perylene black (PBk31, PBk32) assumes a black color in spite of having a skeleton slightly different from that of a perylene pigment. It is known as a heat shielding black pigment, because it does not absorb infrared radiation.
This perylene black which does not absorb infrared radiation is therefore superior to carbon black in heat shielding effect. Its heat shielding effect is however insufficient, because it cannot reflect all the infrared rays and permits transmission of some of them through the film.
The perylene black has a dark chestnut color tone so that it is inferior in jet blackness level and therefore, aesthetic quality of black color to carbon black. Perylene black was therefore not employed for industrial products in which aesthetic quality is required, for example, automobiles and motorbikes and its use was limited to special purposes.
Use of a color clear coating for heightening jet blackness degree of the resulting film has already been reported. For example, a method of applying a color clear coating of a black dye onto a black color base or applying a color clear coating containing carbon black to a dark metallic color is published in Japanese Laid-Open Patent Publication No. H11-104563 (1999). These inventions are however insufficient from the viewpoint of a heat shielding effect.
In Japanese Laid-Open Patent Publication No. H11-302549 (1999) are disclosed inventions relating to an infrared reflective composition containing 0.1 percent by weight or less of carbon black as a coloring component in the resin composition and a pigment and/or dye having infrared reflection and/or infrared transmission characteristics with slight infrared absorption; and an infrared reflector essentially provided with a first layer composed of a resin composition with slight infrared absorption and an infrared reflective component and a second layer which is formed over the first layer and substantially transmits or reflects infrared rays.
The above-described invention does not include any specific example of a dye excellent in heat shielding effect. Moreover, it does not include any description about effects of having a color clear layer containing a dye for attaining both heat shielding property and jet black color tone. Even if a dark color tone is available by using “infrared reflective layer plus infrared transmitting layer” in combination, it is insufficient for attaining both a heat shielding effect and “jet blackness with clearness”.
In Japanese Laid-Open Patent Publication No. 2002-60698, disclosed is an invention of actualizing various color tones including dark color while maintaining a high infrared reflectance as a whole by disposing an infrared reflecting layer having a high infrared reflectance and an infrared transmitting layer obtained using an infrared transmitting layer-forming composition which contains a resin component and a pigment showing 50% or less absorptance of infrared rays having a wavelength of from 800 to 1600 nm.
Use of “infrared reflecting layer plus infrared transmitting layer” in combination according to the above-described invention is insufficient for actualizing both heat shielding effect and “jet blackness with clearness”.
There is accordingly a demand for a method of forming a film having both a heat shielding effect and jet blackness with transparent clearness; and a film structure obtained by the film forming method.